Compositions and process for the electrodeposition of metals

ABSTRACT

A cyanide free electrolyte for the electrodeposition of metals comprises an aqueous solution of (a) a metal ion, (b) a cyanidine compound and optionally, (c) a phosphonic acid compound.

United States Patent [1 1 Kowalski [451 Apr. 22, 1975 1 COMPOSITIONS ANDPROCESS FOR THE ELECTRODEPOSITION OF METALS [75] Inventor: XavierKowalski, Saint Louis. Mo.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Jan. 10, 1974 [21] Appl. No.: 432,377

[52] U.S. Cl 204/52 R; 204/D1G. 2; 204/43 R. 204/44; 204/45 R; 204/46 R;204/46 G; 204/48; 204/49; 204/50 R; 204/51; 204/54 L.

204/55 R [51] Int. Cl. C23b 5/02; C23b 5/18; C23b 5/46 [58] Field ofSearch 260/248 A, 248 R.

204/52 R, 52 Y, 45 R, 45 M, 45.5, 46 R, 46 G, 47, 48, 49, 50 R, 50 Y,51. 53,54 R, 54 L, 55 R, 55 Y, 43, 44, 1.5

[56] References Cited UNITED STATES PATENTS 2,849,352 8/1958 Kirstahlerct a1, 204/44 OTHER PUBLICATIONS B. Egeberg et 11]., Trans. Electrochem.Soc., vol. 66, pp. 211-227, (1938).

Primary Examiner-G. L. Kaplan Attorney, Agent, or Firm-W. R. Eberhardt;T. B. Leslie [57] ABSTRACT A cyanide free electrolyte for theelectrodeposition of metals comprises an aqueous solution of (a) a metalion, (b) a cyanidine compound and optionally, (c) a phosphonic acidcompound.

16 Claims, No Drawings COMPOSITIONS AND PROCESS FOR THEELECTRODEPOSITION OF METALS BACKGROUND OF THE INVENTION l. Field of theInvention The present invention relates to the electrodeposition orelectroplating of metals, and to the composition of the electroplatingbath from which the metal is deposited. More particularly. the presentinvention relates to electrolyte compositions useful as a strike bathfor copper and other metals.

2. Description of the Prior Art The electrodeposition of metals fromaqueous solutions of metal ions is an old art. The typicalelectroplating system consists of an electroplating bath and two or moreelectrodes. The cathode of the electrode system is the object to beplated. The anode may be carbon or a solid piece of the metal to beplated upon the cathode, A solid metal anode is consumed in the electro-7 Copper (as metal) 1.8 -3.5 oL/gal Free cyanide .75-1 .5 do. Rochellesalt 2 5 do. Soda ash 2 8 do. pH ll.5 I2.5 do. CD. l575 amptlftfTemperature l-l40F.

Time /1-3 minutes. depending on CD. used In making the copper strike,the current must be on when the parts are immersed in the solution.Following the copper strike. the parts are transferred to the regularcopper plating bath for the balance of the copper deposit.

Electroplating baths and strike baths comprising aqueous alkalinesolutions of metal cyanides have several disadvantages associated withthe toxic nature of cyanide. The use of metal cyanide solutions can behazardous if the pH of the electroplating medium should drop to neutralor below since there is a danger of poisonous hydrogen cyanide gas beingproduced. Also, the Toxic metal cyanides present a disposal problem, andremoving cyanides from used baths prior to disposal requires specialequipment and adds to the cost of the electroplating operation.

The prior art has suggested certain techniques for electroplatingwithout the use of cyanides. US. Pat. No. 3,475,293, for example,suggests the use of certain diphosphonates or monoamino lower alkylenephosphonates in electroplating divalent metal ions. US. Pat. Nos.3,706,634 and 3,706,635 suggest combinations of ethylene diaminetetra(methylene phosphonic acid). l-hydroxy ethylidene-l,l-diphosphonicacid, and amino tri(methylene phosphonic acid) as particularly usefulcomplexing compositions. US. Pat. No. 3,6l7,343 is similarly directedtoward a nickel plating system employing certain phosphonic acidcompounds.

While the cyanide'free electroplating systems of the prior art aresuitable for some plating operations. there is a tendency for immersionplating to occur on iron or zinc base stocks unless a metal strike isfirst applied. Metal deposited by immersion is spongy and adheres poorlyso that subsequent metal deposited electrically has a tendency to crackand peel. It is accordingly an object of the present invention toprovide a cyanidefree electrolyte composition suitable for use as astrike bath for depositing copper and other metals directly onto iron orzinc. It is a further object of the present invention to provide amethod and cyanide-free electrolyte composition for electricallydepositing metallic copper from a solution containing monovalent copperCu(l).

SUMMARY In accordance with the present invention there is employed asthe electroplating bath an aqueous solution comprising (a) from 0.01 toabout 5 percent by weight of a monovalent, divalent or polyvalent metalion; (b) from about 0.0] percent to the solubility limit of a cyanidinecompound containing the ring radical and optionally (c) anorganodiphosphonic acid compound having the structure wherein M ishydrogen, alkali metal or ammonium, and R is an alkyl, alkylene oralkylidene radical having from 1 to 11 and preferably from 1 to 5 carbonatoms optionally substituted with OH or halide. Such electroplating bathcompositions are useful in plating metals at a pH of from about 7 to 12and at a temperature of from about 30 to C.

DESCRIPTION OF PREFERRED EMBODIMENTS In a preferred embodiment of thepresent invention, a thin deposit of copper is electrically plated uponactive base metals from a cyanide-free strike bath comprising monovalentcopper Cu(l). While the ensuing description is directed primarily towardthe plating of copper on zinc, it is contemplated that metals other thancopper, particularly silver, tin, nickel, chromium and gold are alsodeposited in a like manner on zinc and other active base metals such asaluminum, magnesium and iron in accordance with the method and teachingof the instant invention.

Cyanidine compounds useful in the practice of the present invention arethose compounds containing the trivalent ring radical where X is anycation which will render the compound at least slightly soluble in theelectroplating bath composition. Preferably, X is selected from thegroup consisting of OM, halogen. -NH- and mixtures thereof, where M ishydrogen. alkali metal or ammonium. Most preferably, X is -OM and thecyanidine compound is cyanuric acid or an alkali metal salt thereof.

Organodiphosphonic acid compounds useful in the practice of the instantinvention are those compounds having the general structure where R is analkyl, alkylene or alkylidene radical of from 1 to about 11 andpreferably from 1 to about 5 carbon atoms, or a said radical substitutedwith hydroxy or halide, and each M is individually hydrogen, alkalimetal, or ammonium ions. Examples of preferred compounds include, butare not limited to, methylene diphosphonate, l.l-ethylene diphosphonate,l-hydroxy ethylidene-l l -diphosphonate, and l-chloroethylidenel, l-diphosphonate.

The electroplating bath or electrolyte of the present inventioncomprises an aqueous solution of the metal to be plated. the cyanidinecompound. pH adjusters and optionally one or more additives includingbrighteners, buffering agents, levelers, and organodiphosphonic acidcompounds which are intended to improve the performance or life of thebath or the quality of the metal deposit. or to impart other beneficialeffect. It is common in the electroplating art to utilize many andvaried additives which are selected by the skilled electroplateraccording to the particular system being used. The use of such additivesin the electroplating bath compositions of the present invention inorder to adapt these compositions to individual circumstances areincluded within the scope of the present invention.

The bath is prepared according to conventional techniques by simplydissolving the desired ingredients into a quantity of water. The wateris preferably low in mineral content and may be deionized. The metal tobe plated is often added in the form ofa water soluble salt such as ametal sulfate, chloride, phosphate, citrate, carbonate or acetate.Carbonate and acetate salts are often preferred because the anions ofthese salts may be thermally decomposed and thereby removed from thebath when the metal ion is released. In preparing a bath for copperstriking, monovalent copper is most conveniently added as cuprouschloride.

The optimum concentration of metal salt and cyanidine compound in theelectroplating bath will be largely determined by the identity of themetal and by the characteristics of the individual electroplatingsystem. As a rule, the concentrations are limited primarily by thesolubilities of the compounds. As an example, in a copper strike bathbased upon Cu(l) there is usually employed from about 0.01 percent toabout 0.5 percent by weight of metal in solution and from about 0.0l toabout 0.25 percent by cyanuric acid, the maximums being the respectivesolubility limits. When plating Cu(ll) or other more soluble metals, themetal ion concentration may be increased to 5% or higher.

The copper strike bath is generally operated within a pH range of fromabout to 12. The optimum pH will depend to some extent upon thecomposition of the particular bath. Since pH is easily adjusted by theaddition of alkaline materials such as alkali metal hydroxides, or acidmaterials such as mineral acids, it is a relatively simple matter toadjust the pH in either direction until optimum plating characteristicsare achieved. As

a general rule it is often found that higher pH values, that is withinthe range of from about 1 l to 12, give better results when strikingcopper from Cu(l) than lower pH levels although exceptions to this rulemay be found.

The use of the organodiphosphonic acid compound as defined above isfound to enhance the performance of the electroplating bath,particularly with respect to depositing copper. A combination ofcyanuric acid and l,l-ethylene diphosphonic acid (EDP) is particularlyeffective to produce bright, uniform, and tightly adhering deposits ofcopper on brass, zinc and steel by striking at a pH of about 11.5. Theconcentration of EDP used in the composition of this invention issufficient to provide a mole ratio of EDP to copper of from about 0.5:1,although from about 1:1 to about 2:1 is preferred.

While the aforegoing description is directed primarily to thecomposition of the electroplating or strike bath, the present inventionfurther provides a process for the electrodeposition of monovalent,divalent or trivalent metals which comprises the steps of electrolyzingan aqueous solution of any of the metal ions hereinbefore described, acyanidine compound, and any of the optional additives hereinbeforedescribed. By the process of this invention, metal such as copper, iron,nickel, zinc and cadmium may be electrically deposited upon a cathodesuch as steel, aluminum, brass, zinc and the like with little or nochemical deposition.

During the electrodeposition process, the electroplating bath ismaintained at a temperature within the range of the freezing point toboiling point of the bath, generally within a range of from about 30C.to about 90C. For reasons of current efficiencies it has been foundpreferable to maintain the temperature of the electroplating bath withinthe range from about 40C. to about C.

The amount of current employed in the electrodeposition may vary widely,depending upon the particular metal being plated, the temperature of thebath and whether or not the bath is agitated duringthe electroplatingprocess. In general, the amount of current employed will be sufficientto provide a current density of from about 1 to 300 amperes per squarefoot of electrode surface. Ordinarily when the electroplating bath isquiescent or unagitated, the current density will be in the range offrom about 15 to amperes per square foot, while when the electroplatingbath is agitated current densities up to about amperes per square footmay be utilized. The optimum or preferred currentdensity for anyparticular electroplating situation will depend upon the individualcharacteristics of the operation and is readily determined by employingconventional electroplating techniques.

The time required to electroplate or to electrically deposit the metalwill vary with the kind of metal, the current density, and bathcomposition and concentration, as well as upon the thickness of theplate or deposit desired. Generally, the greater the current density,the shorter will be the time required to produce a metal strike or aplate of a given thickness.

In accordance with a preferred embodiment of the present invention, acopper strike is electrically deposited upon a wide variety of basemetals or substrates such as zinc, iron, brass, steel, aluminum and thelike. This preferred process comprises passing an electric current, at adensity in the range of from about 15 to about 75 amperes per squarefoot of cathode surface. through an aqueous solution containingmonovalcnt copper ions and cyanuric acid or a mixture of cyanuric acidand EDP and having a pH in the range of from about 10.0 to about 12.0and preferably about 11.5. The concentration of copper in theelectroplating bath composition is preferably from about 0.01 to about0.5 percent by weight, based on the weight of the solution. Thetemperature of the solution is preferably maintained within the range offrom about 40C. to about 70C. during the electroplating operation.

As stated above, the electroplating and strike solutions of the presentinvention can contain known brighteners, buffers, and leveling agentsand other additives commonly used in electroplating operations. Boricacid and its salts are compatible buffers for many formulas of theinvention, and selenites and arsenites are useful brighteners for copperplating baths while aldehydes and ketones are useful for zinc plating.Other additives which may be employed in the electroplating solutions ofthe present invention include those disclosed in the 39th Annual Editionof Metal Finishing Guidebook Directory, 1973, published by Metals andPlastics Publications. Inc., 99 Kinderkamack Road, Westwood, NJ.

Certain preferred embodiments of the present invention concerning theelectrodeposition of copper as illustrated by the following Exampleswhich are not limiting of the invention. All parts and percentages areby weight unless otherwise specified. Plating tests were conductedaccording to conventional procedures in a Hull Cell.

The Hull Cell is constructed substantially as the electrolysis celldescribed in US. Pat. No. 2,149,344. This type of Hull Cell is standardequipment for the evaluation of electroplating solutions by thesubjective determination of brightness rating as based on the width ofthe brightness range, uniformity of brightness, and the presence orabsence of smudges, stains and discoloration. ln addition, theeffectiveness of the bath is also evaluated on the basis of adhesion ofplated metal to the cathode. The particular cathodes utilized in thistest were brass or zinc as indicated and were each 5 X 3-% inches insize. The anode utilized in these tests was made of copper and was 2-% X2- /8 inches in size. The Hull Cell utilized in this test had a capacityof 1,000 milliliters.

EXAMPLE 1 An electrolyte was made according to the followingformulation:

0.99 g. C uC 1 12 g. CYA (cyanuric acid) 300 ml. DI. Water EXAMPLE 1] Anelectrolyte was made according to the following formulation:

1.5 g. CuCl 20 g. K- ,HCYA (partial K salt of CYA) 5 g. NaH-.CYA(partial Na salt of CYA) 5 g. EDP.-l Na (Na salt of 1.1-ethylenediphosphonic acid) 301) ml. D. 1. Water The pH was adjusted to l 1.5 bythe addition of NaOH and the solution filtered to remove undissolvedsolids. A brass panel was cleaned and plated in the Hull Cell at 1 amp.for 2 minutes at 45C. A very good bright deposit of copper was obtained.

A zinc panel was cleaned and immersed in the solution for 30 seconds at45C. No evidence of immersion plating was observed. The zinc panel waselectroplated in the Hull Cell at 1 amp. for 2 minutes at 45C. A verygood, thin deposit of copper was obtained.

EXAMPLE Ill An electrolyte was made according to the followingformulation:

1 g. CuCl 12.6 g. Melamine 12 g. NaOH 10 g. EDPA Na 200 ml. D,l. WaterThe pH was adjusted to l 1.0 by the addition of orthophosphorus acid,and the solution filtered to remove undissolved solids. Brass and zincpanels were individually cleaned and plated in the Hull Cell at 1 ampfor 2 minutes at 35C. The copper depositions were judged as fair to goodin brightness and uniformity. No immersion plating was observed.

Although the invention has been illustrated by reference to theelectrodeposition of copper and particularly copper striking utilizingthe method and compositions of this invention, the present invention isnot limited thereto but is also useful in electrodepositing other metalsupon other cathode materials as hereinabove described. Accordingly, thepresent invention is not to be limited except as defined in the claimsappended hereto.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A cyanide-free process for the electrodeposition of monovalent,divalent and polyvalent metal ions which comprises the steps ofelectrolyzing an aqueous solution comprising a. a monovalent, divalentor polyvalent metal ion,

and

b. a cyanidine compound having the general formula c N c C \N x c \N \Nc c -x wherein X is selected from the group consisting of -OM, --NH andhalogen ions, where M is hydrogen or alkali metal ion, the concentrationof (a) in said aqueous solution being from about 0.01 percent to 5percent; the concentration of (b) being from about 0.01 percent to thelimit of solubility; the pH of said aqueous solution being from about 7to 12, and the temperature of said aqueous solution being from about 30to 90C.

2. A process of claim 1 wherein said aqueous solution comprises. inaddition to (a) and (b). a compound (c) having the structure wherein Mis hydrogen. alkali metal or ammonium ion, and R is selected from thegroup consisting of alkylene or alkylidene radical having from 1 toabout 1 1 carbon atoms and hydroxy and halogen substituted derivativesthereof, in a concentration sufficient to provide a mole ratio of atleast about 0.511 of (c) to (a).

3. A process of claim 2 wherein said compound (c) is l.l-ethylenediphosphonic acid.

4. A process of claim 3 wherein (b) is cyanuric acid or an alkali metalsalt thereof.

5. A process of claim 4 wherein said metal ion (a) is monovalent Cu(l).the concentration of said metal ion is from about 0.01 to about 0.5percent by weight, and the pH of said aqueous solution is from about I lto 12.

6. A process of claim 1 wherein said metal ion (a) is monovalent Cu(l).the concentration of said metal ion is from about 0.0l to about 0.5percent by weight and the pH of said aqueous solution is from about l lto 12.

7. A process of claim 6 wherein (b) is cyanuric acid or alkali metalsalts thereof.

8. A process of claim 1 wherein said metal ion (a) is selected from thegroup consisting of copper, iron, nickel. zinc. cadmium. tin. silver,chromium and gold.

9. A cyanide-free electroplating bath composition comprising an aqueoussolution of a. from about 0.01 to about percent by weight of amonovalent. divalent or polyvalent metal ion, and

b. from about 0.0l percent to the solubility limit of a cyanidinecompound having the general formula wherein M is hydrogen, alkali metalor ammonium ion, and R is selected from the group consisting of alkyleneor alkylidene radical having from 1 to about 1 1 carbon atoms. andhydroxy and halogen substituted derivatives thereof, in a concentrationsufficient to provide a mole ratio of at least about 0.521 of (c) to(a).

11. A composition of claim 10 wherein (b) is cyanuric acid or an alkalimetal salt thereof.

12. A composition of claim 11 wherein said metal ion (a) is monovalentCu(l) and the concentration of said metal ion is from about 0.01 toabout 0.5 percent by weight.

13. A composition of claim 10 wherein said compound (c) is l,l-ethylenediphosphonic acid.

14. A composition of claim 9 wherein (b) is cyanuric acid or alkalimetal salts thereof.

15. A composition of claim 14 wherein said metal ion is monovalent Cu(l)and the concentration of said metal ion is from about 0.01 to about 0.5percent by weight.

16. A composition of claim 9 wherein said metal ion (a) is selected fromthe group consisting of copper. iron, nickel, zinc, cadmium, tin,silver. chromium and gold.

UNITED STATES PATENT OFFICE @EHMQATE 0F coEeTwN a PATENT NO. 3,879,270

DATED April 22 1975 tNVENTOR S Xavier Kowalski It is certified thaterror appears in the ab0veidentihed patent and that sald Letters Patentare hereby corrected as shown below: O

Claim 9 column 8 line 9 "-OH should be OM,

Q fined an fif ii of August 1975 [SEAL] Arresr:

RUTH c. MASON c. MARSHALL DANN Arresting Officer (mmnissimu'r uj'lulcnlxand Trademarks

1. A cyanide-free process for the electrodeposition of monovalent,divalent and polyvalent metal ions which comprises the steps ofelectrolyzing an aqueous solution comprising a. a monovalent, divalentor polyvalent metal ion, and b. a cyanidine compound having the generalformula
 1. A CYANIDE-FREE PROCESS FOR THE ELECTRODEPOSITION OFMONOVALENT, DIVALENT AND POLYVALENT METAL IONS WHICH COMPRISES THE STEPSOF ELECTROLYZING AN AQUEOUS SOLUTION COMPRISING A. A MONOVALENT,DIVALENT OR POLYVALENT METAL ION, AND B. A CYANIDINE COMPOUND HAVING THEGENERAL FORMULA
 2. A process of claim 1 wherein said aqueous solutioncomprises, in addition to (a) and (b), a compound (c) having thestructure M2O3P - R - PO3M2 wherein M is hydrogen, alkali metal orammonium ion, and R is selected from the group consisting of alkylene oralkylidene radical having from 1 to about 11 carbon atoms and hydroxyand halogen substituted derivatives thereof, in a concentrationsufficient to provide a mole ratio of at least about 0.5:1 of (c) to(a).
 3. A process of claim 2 wherein said compound (c) is 1,1-ethylenediphosphonic acid.
 4. A process of claim 3 wherein (b) is cyanuric acidor an alkali metal salt thereof.
 5. A process of claim 4 wherein saidmetal ion (a) is monovalent Cu(I), the concentration of said metal ionis from about 0.01 to about 0.5 percent by weight, and the pH of saidaqueous solution is from about 11 to
 12. 6. A process of claim 1 whereinsaid metal ion (a) is monovalent Cu(I), the concentration of said metalion is from about 0.01 to about 0.5 percent by weight and the pH of saidaqueous solution is from about 11 to
 12. 7. A process of claim 6 wherein(b) is cyanuric acid or alkali metal salts thereof.
 8. A process ofclaim 1 wherein said metal ion (a) is selected from the group consistingof copper, iron, nickel, zinc, cadmium, tin, silver, chromium and gold.9. A cyanide-free electroplating bath composition comprising an aqueoussolution of a. from about 0.01 to about 5 percent by weight of amonovalent, divalent or polyvalent metal ion, and b. from about 0.01percent to the solubility limit of a cyanidine compound having thegeneral formula
 10. A composition of claim 9 comprising in addition to(a) and (b), a compound (c) having the structure M2O3P - R - PO3M2wherein M is hydrogen, alkali metal or ammonium ion, and R is selectedfrom the group consisting of alkylene or alkylidene radical having from1 to about 11 carbon atoms, and hydroxy and halogen substitutedderivatives thereof, in a concentration sufficient to provide a moleratio of at least about 0.5:1 of (c) to (a).
 11. A composition of claim10 wherein (b) is cyanuric acid or an alkali metal salt thereof.
 12. Acomposition of claim 11 wherein said metal ion (a) is monovalent Cu(I)and the concentration of said metal ion is from about 0.01 to about 0.5percent by weight.
 13. A composition of claim 10 wherein said compound(c) is 1,1-ethylene diphosphonic acid.
 14. A composition of claim 9wherein (b) is cyanuric acid or alkali metal salts thereof.
 15. Acomposition of claim 14 wherein said metal ion is monovalent Cu(I) andthe concentration of said metal ion is from about 0.01 to about 0.5percent by weight.